1. Field of the Invention
This invention relates to a shield structure of a helmet, and more particularly to a shield installed outside a front opening formed in a helmet.
2. Description of the Prior Art
As a shield installed on a helmet, a single sheet type synthetic resin plate (for example, a plate member of polycarbonate resin) is generally used. Such a shield is used to protect the face of a person wearing the helmet from blowing rain, wind, dust, insects and small stones or the like. When used in rain, the shield will be fully closed over the front opening in the helmet.
However, when the shield is used in a closed state, it can become fogged by the user's breath or by sweat caused by an increased temperature within the helmet or the like.
This shield misting condition is produced by a temperature difference across the shield, wherein due to this fact, as means for reducing the temperature difference across the shield, a ventilation means is utilized for taking surrounding atmosphere into the inside part of the helmet and directing the air along the inner surface of the shield, thereby its corresponding effects realized. However, this system provides a device for taking in the surrounding atmosphere into the helmet itself, resulting in the productivity or design of the helmet being affected. Due to this fact, it has been required to provide a shield capable of accomplishing a complete anti-misting situation only with the shield and without influencing the construction of the helmet.
As the anti-misting structure completely finished only with this shield, there has been provided an integral shield having a dual-structure.
The configuration is made such that a seal member is adhered and fixed along a substantial outer circumference of a visual range between an inner plate and an outer plate so as to form a closed space forming a heat insulated layer between the inner plate and the outer plate, wherein a temperature difference across the plates per one shield is reduced and an anti-misting against the inner plate of the shield is performed.
However, since the aforesaid anti-misting structure for the shield is made such that an inner plate and an outer plate are adhered to each other and assembled integrally to form a closed space, it is hard to keep its durability while assuring an air-tightness by holding a desired curve and its manufacturing cost is also high due to the aforesaid form. In addition, in the case that a seal member for use in forming a closed space between the inner plate and the outer plate is deteriorated to cause the air-tightness to be damaged due to damage or the like, it is impossible to perform a partial replacement of the member to return it to have an initial function and there may be provided a disadvantage that the entire assembly must be broken to replace the broken assembly with a new shield. Further, in order to improve an effect of anti-misting state in response to a surrounding circumstances, it is also impossible for a user by himself or herself to apply an anti-misting processing such as a coating of surface active agent or the like at both inside part of the outer plate and outside part of the inner plate.